Recently, successful tests have been conducted to make the exhaust gases from Otto engines less environmentally harmful in their composition, by at least partial replacement of gasoline. The possibility of operating engines at least partially with hydrogen has been described in several publications, such as "Hydrogen as an Alternative Fuel for Otto Engines" by H. Buchner and H. Saufferer in ATZ 4/76 and "Prototype Hydrogen Automobile Using a Metal Hydride" by D. L. Hendriksen, D. B. Mackay, V. R. Anderson, Billings Energy Research Corporation in Conference Proceedings of the First World Hydrogen Energy Conference, March 1976, Miami, 7c 1-12.
Until recently, the main obstacle to using hydrogen-powered vehicles was the voluminous, dangerous, and energy-consuming storage of hydrogen in the gaseous or liquid form. Only the development of suitable metal hydride reservoirs has made hydrogen drive significant once more.
These metal hydrides can be classified roughly into two groups, namely the so-called low-temperature hydrides (LT hydrides) and high-temperature hydrides (HT hydrides). The release of hydrogen from the hydrides is an endothermal reaction, while storage is an exothermal reaction. The hydrogen must have a pressure of at least 1 bar so that it can be fed to the engine without using a compressor; the equilibrium temperature, at which this pressure is obtained above the hydride reservoir, in the case of LT reservoirs, ranges from less than 0.degree. C. to temperatures equal to or slightly above room temperature, while these temperatures are at 200.degree. C. or more in HT reservoirs.
The heat of liberation for H.sub.2 can be supplied in the case of LT reservoirs for example by the radiator water or the ambient air, while in HT reservoirs the exhaust heat can be used for this purpose (as shown in FIG. 2).
According to a previous proposal, the heat required to release the hydrogen from LT reservoirs is drawn from the ambient air, and this heat requirement is used to cool the interiors of motor vehicles.
It has been found that the heat capacity of heated hydride reservoirs can also be used for heating purposes without influencing the functioning ability of the reservoir for motor operation.